Error encoding method and apparatus for satellite and cable signals

ABSTRACT

A signal distribution system and method distributes an error-encoded satellite communication signal over a cable network to a number of receiver units within a multiple dwelling unit. The system and method receives and decodes the satellite communication signal to produce a data signal and an error indication that indicates whether an uncorrected transmission error is present in the data signal. The error indication is then combined with the data signal and an information signal to produce a combined signal which is then error encoded and transmitted over the cable network to the receiver units. The receiver units decode the combined signal to produce the data signal, the information signal, the error indication and a further error indication that indicates whether the data signals have experienced an uncorrected error during communication over the cable network. The receiver units use both the error indication and the further error indication to determine if the received data signal has one or more errors therein.

RELATED APPLICATIONS

This is a continuation of U.S. provisional patent application Ser. No.60/104,601, entitled “Error Encoding Method And Apparatus For SatelliteAnd Cable Signals,” filed Jan. 27, 1998 (now abandoned); which was acontinuation of non-provisional U.S. patent application Ser. No.09/014,299, entitled “Error Encoding Method And Apparatus For SatelliteAnd Cable Signals,” filed Jan. 27, 1998 (now abandoned); which is acontinuation-in-part of U.S. patent application Ser. No. 08/787,336entitled “Transmodulated Broadcast Delivery System For Use In MultipleDwelling Units”, filed Jan. 27, 1997.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates generally to signal distribution systemsand, more particularly, to audio/visual/data signal distribution systemsthat distribute satellite signals typically in conjunction with standardterrestrial and/or cable signals to a plurality of individual receiverswithin one or more multiple dwelling units.

(b) Description of Related Art

Audio/visual/data (A-V) signal distribution systems generally rely oneither a cable network or on free-space propagation for delivering A-Vsignals, such as television signals, to individual users or subscribers.Cable-based A-V signal distribution systems transmit one or moreindividual A-V signals or “channels” over wire, while free-spacepropagation systems transmit one or more channels over-the-air, i.e., ina wireless manner. Most large-scale cable and wireless signaldistribution systems broadcast a broadband A-V signal having a pluralityof individual A-V signals modulated onto one or more carrier frequencieswithin a discernable frequency band.

Some wireless signal distribution systems use one or more geosynchronoussatellites to broadcast a broadband A-V signal to receiving units withina large geographic area while other wireless systems are land-based,using one or more land-based transmitters to broadcast to individualreceiver units within smaller geographic areas or cells. A satellite A-Vsignal distribution system generally includes an earth station thatcompiles a number of individual A-V programs into a broadband signal,modulates a carrier frequency band with the broadband signal and thentransmits (uplinks) the modulated signal to one or more geosynchronoussatellites. The satellites amplify the received signals, shift thesignals to different carrier frequency bands and transmit (downlink) thefrequency shifted signals to earth for reception at individual receivingunits.

The uplink and downlink broadband signals of analog satellite systemsare typically divided into plurality of transponder signals, eachtypically containing a single analog signal. For example, analogsatellite systems operating in the so-called “C-band,” i.e., between 3.7GHz and 4.2 GHz, may broadcast a plurality of transponder signals, eachincluding a single frequency modulated analog T.V. channel. In currentdigital satellite systems, each transponder typically contains a numberof individual channels multiplexed into a single data stream, commonlyreferred to as a program multiplex. Satellite systems may also broadcasta set of transponder signals at multiple polarizations, for example, ata right-hand circular polarization (RHCP) and at a left-hand circularpolarization (LHCP), within the band of carrier frequencies associatedwith the satellite, effectively doubling the number of channelsbroadcast by the system.

Satellite signal distribution systems exist for many frequency bands,including the so-called “Ku-band.” One known Ku-band direct-to-homesatellite system now in operation uses an uplink signal having 16 RHCPtransponder signals and 16 LHCP transponder signals modulated ontofrequency bands between about 17.2 GHz and about 17.7 GHz. Each of these32 transponder signals is program-multiplexed to include digital datapackets associated with e.g. about five to eight or more individual A-Vprograms, such as television channels, and is modulated according to aquartenary phase shift keying (QPSK) modulation scheme. The satellitesassociated with this system shift the uplink transponder signals tocarrier frequencies ranging from approximately 12.2 GHz to approximately12.7 GHz and transmit these frequency-shifted transponder signals backto earth for reception at each of a plurality of individual receiverunits.

At the individual receiver units, a receiving antenna, typicallycomprising a parabolic dish antenna, is pointed in the general directionof the transmitting satellite (or other transmitting location) toreceive the broadband QPSK modulated multiplex of A-V signals.Typically, such antennas include a low noise block (LNB) whichamplifies, filters and shifts the incoming signal to an intermediatefrequency band, such as L-band (between about 1.0 GHz and 2.0 GHz). Therepresentative system, in particular, shifts the satellite signal to thefrequency band between about 950 MHz and about 1450 MHz.

Typically, only the RHCP transponder signals or the LHCP transpondersignals are mixed down to L-band, depending on which particular A-Vchannel a user is viewing. However, in systems having a two-channel LNB,both the RHCP and the LHCP transponder signals may be individuallyshifted down to a 500 MHz portion of L-band (e.g. between 950 MHz and1450 MHz) and provided, via separate lines, to a set-top box or otherintegrated receiver/decoder (IRD) associated with the receiver unit. Atthe IRD, an A-V program associated with a particular channel within oneof the program-multiplexed transponder signals is decoded and providedto a television or other presentation or processing device for displayand/or for processing of transmitted data, audio output, etc. However,because cable lines are inherently frequency limited, typical cablesused at receiver sites (such as RG-6 and RG-59) are not capable ofsimultaneously transmitting all of the received satellite signals (1000MHz) along with standard CATV signals to the IRD.

Furthermore, the receiving antennas or dishes associated with land-basedor satellite-based wireless signal distribution systems are typicallylarge and cumbersome. For example, C-band satellite dishes are generallyin the range of four to five feet in diameter and, therefore, require alarge amount of operating space. As a result, it can be difficult, ifnot practically impossible, to install a receiving antenna for eachindividual unit within a multiple dwelling unit (MDU), such as anapartment, condominium or townhome complex. Reception of a particularsatellite signal is made even more difficult in MDUs when, as isgenerally the case, some of the individual dwelling units therein do nothave any walls or outside exposure facing the direction in which thereceiving antenna must be pointed, or these dwelling units are shadowedby surrounding buildings or other obstructions.

In the past, these disadvantages have been overcome by placing one ormore receiving antennas on, for example, the roof of an MDU and thenrunning cable to each of the individual dwelling units. For example, asystem for redistributing a single, off-air signal to multiple buildingsin a small geographic area is disclosed in Japanese Patent Document No.56-47183. However, common L-band multi-user distribution solutionstypically used to support single dish antenna systems are fraught withinstallation and maintenance problems. For example, significant roll-offor degradation of the television signals may occur in cable systems dueto the poor high frequency propagation properties of standard cablelines especially at and above L-band. Broadcasting a received broadbandA-V signal over an existing cable network at lower carrier frequenciesmay prevent the use of that network for other A-V signals, such asstandard cable, CATV, UHF and VHF television signals, or may requirethat some of the broadband signals or existing cable signals beeliminated due to the bandwidth restrictions of the cable network.

One system proposed by the European Telecommunications StandardsInstitute (ETSI) in the area of Satellite Master Antenna Television(SMATV) receives a QPSK modulated satellite television signal (which maybe combined with terrestrial TV signals) and remodulates this signalaccording to a 64 quadrature amplitude modulation (64-QAM) technique.The SMATV system then sends this remodulated signal out over cable toone or more adjacent buildings. Likewise, U.S. Pat. No. 5,173,775discloses a system that remodulates data portions of a satellitetelevision signal from one modulation scheme to another, such as from FMto AM, for retransmission to subscribers. However, these systems do notspecifically demonstrate how to propagate remodulated satellite signalsand existing cable or terrestrial signals on the same cable line orother transmission channel in an efficient manner or demonstrate how toremodulate and broadcast a large number of transponder signalsassociated with one or more satellites over the same cable line or othertransmission channel to one or more adjacent buildings.

SUMMARY OF THE INVENTION

The present invention relates to a system and method for redistributinga communication signal received from, for example, a satellite, over acommunication channel, such as a cable network, to one or more receiverunits within one or more MDUs. The inventive system and method allowerror-encoding techniques to be performed to the communication signal inboth the satellite and the cable transmission stages and detectsuncorrected errors that occur within the redistributed communicationsignal in either or both of the satellite and cable transmission stages.The inventive system and method also allow a separate communication orinformation signal to be placed on the cable network to inform areceiver unit of, for example, information related to the decoding ofthe distributed communication signal.

According to one aspect of the present invention, a signal distributionsystem for distributing an error-encoded communication signal over acommunication channel includes a receiver that receives a firsterror-encoded communication signal and a decoder that decodes thereceived first error-encoded communication signal. The decoder producesa data signal and an error indication that indicates whether anuncorrected transmission error is present in the data signal. A signalencoder produces a second error-encoded communication signal havinginformation related to both the data signal and the error indication. Atransmitter transmits the second error-encoded communication signal overthe communication channel, which may be a cable network, to one or morereceiver units.

Each receiver unit includes a decoder that decodes the seconderror-encoded communication signal received from the cable network toproduce the error indication, the data signal, and a further errorindication that indicates whether an uncorrected error is present in thedata signal as a result of transmission over the cable network. An errordetector detects the presence of an error within the data signal basedon the error indication and the further error indication.

Preferably, the data signal includes a plurality of first data packetsof a first length, the decoder includes a device that produces aseparate error indication for each of the plurality of first datapackets, and a repacketizer includes a device that develops amultiplicity of second data packets of a second length, each of whichincludes a portion of one or more of the first data packets and theseparate error indications. Each first data packet may be one hundredand thirty bytes in length while each second data packet may be onehundred and eighty-seven bytes in length.

Still further, a signal generator may be used to generate an informationsignal known as side data associated with each of the first data packetsand this information signal may be combined with the first data packetsand the separate error indications to produce the combined signal. Ifdesired, the information signal may include information pertaining tothe decoding of the second error-encoded communication signal or anyother desired information to be passed from a transmodulator to a user'sIRD. Examples include, without limitation, channel set-up information,telephone numbers, a frequency index, mode information for QAMmodulation employed, interleaver depth, error status information,transmodulator configuration, frequency mode, etc. This information maybe arranged in, for example, high, medium and low priority carouselssuch that high priority data is transmitted more frequently than mediumor low priority data, while the lesser priority information istransmitted less frequently.

Other information that may be sent by means of the information signalincludes other status information. In a typical DBS system, such datamay be broadcast on each transponder channel to all receivers tuned tothe transmodulator of the present invention. The primary informationcontained in such side data may include a frequency map of the channelcontent of individual broadcast resources (e.g., frequencies). When areceiver (e.g., an IRD) is powered for the first time, it will not knowwhere in the cable plant frequency spectrum the desired set of channels(e.g. DBS channels) are located. The receiver could ascertain thisinformation by attempting acquisition of signals at each potentialfrequency within the allocated spectrum, until all of a subset ofchannels were located. However, by including a frequency map in the sidedata, this process is substantially expedited. In particular, eachsubscriber module on power-up need only search until it locates a firstof the subset of channels, which will include the side data identifyingthe allocated frequencies for all of the other corresponding channels.By locating a first of the subset of channels, the receiver is thus ableto ascertain immediately the frequency of all of the remaining channels.The side data can also be used to monitor and update this frequency mapas required.

According to a particular aspect of the present invention, a signaldistribution system distributes a communication signal having aplurality of first data packets of a first length over a communicationchannel. The signal distribution system includes a decoder that decodesthe communication signal to produce the plurality of first data packets,a repacketizer that repacketizes the plurality of first data packetsinto a multiplicity of second data packets of a second length that isdifferent than the first length, and a signal encoder that combines themultiplicity of second data packets to form a combined signal. Atransmitter then transmits the combined signal over the transmissionchannel. If desired, information indicating whether an uncorrected erroris present within any of the first data packets and/or informationpertaining to the decoding of the combined signal may be placed in thesecond data packets along with the first data packets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block and partial-schematic diagram of the signaldistribution system according to the present invention;

FIG. 2 is a frequency distribution chart illustrating representativeoptions for transmitting received signals along with existing cableand/or off-air signals over a cable network;

FIG. 3 is a block diagram of an embodiment of the transmodulator of FIG.1 according to the present invention;

FIG. 4 is a block diagram illustrating the satellite decoder of thetransmodulator of FIG. 3;

FIG. 5 is a data chart illustrating the output of the data packetizer ofFIG. 3;

FIG. 6 is a block diagram illustrating an embodiment of the cableencoder of the transmodulator of FIG. 3; and

FIG. 7 is a block diagram of an IRD associated with one of the receiverunits of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

By the way of example only, the signal distribution system of thepresent invention is described herein as redistributing a broadbandKu-band satellite signal (comprising up to 32, QPSK-modulatedtransponder signals transmitted from one or more satellites at a carrierfrequency band centered around approximately 12.45 GHz) to receiverunits within an MDU. It is understood however, that the signaldistribution system of the present invention can be used to redistributeany other type of satellite or land-based wireless signal. The termprogram multiplex (PM) signal is used herein to describe any single ormultiplex of purely visual (such as video), purely audio, or purely datasignals as well as a signal comprising any combination of audio, visual,data or other signals including, for example, television signals,digital data signals, etc.

Referring now to FIG. 1, a signal distribution system 10 according tothe present invention is illustrated for use at a local site having oneor more MDUs and/or other buildings therein. A local site is consideredto be any geographic area of relatively small proportion such as, forexample, a subdivision, a city block, etc., containing one or morebuildings or structures capable of having a plurality of individualreceiving units therein. An MDU may be any type of multiple dwellingunit including, for example, an apartment, townhome, or condominiumcomplex, a hotel/motel, an office building, a recreational or sportsfacility, a cluster of single family homes, a multi-use building and/orany other type of building or structure in which multiple signalreceivers may be located.

The signal distribution system 10 includes a main signal receiver 14disposed on, for example, the roof of an MDU or any other locationcapable of receiving a signal transmitted by a satellite or other signalsource. The signal receiver 14 is preferably in the form of a 24-inchdiameter parabolic dish antenna pointed towards, for example, satellitesthat transmit a Ku-band or other broadband, QPSK-modulated PM signals. Atwo-channel LNB 16 associated with the dish antenna 14 receives themodulated satellite signal reflected from the dish antenna 14. Each ofthe channels of the LNB 16 filters either the RHCP or the LHCP componentof the received signal and mixes this filtered signal down to anintermediate frequency band, for example, the portion of L-band between950 MHz and 1450 MHz. The LNB 16 amplifies and provides the 500 MHz,L-band signals associated with each of the RHCP and LHCP components ofthe downlink signal to a transmodulator 20 via lines 22 and 24,respectively.

Other methods for providing the received QPSK input signals to thetransmodulator 20 may also be used.

The transmodulator 20 remodulates or transmodulates the signals receivedfrom the LNB 16 using an output modulation technique that, preferably,reduces the bandwidth of the signals received from the LNB 16 from two500 MHz bands (i.e., a total of 1000 MHz) to, for example, a single bandof 192 MHz. This reduction in bandwidth may be accomplished by utilizinga more aggressive modulation scheme with appropriate error detection andcorrection codes. The transmodulator 20 then places the transmodulated,reduced-in-bandwidth signal on a cable plant or cable network 26 withinan MDU for distribution to a number of IRDs 30, 32, 34, 36, 38 and 40associated with individual receiver units spread throughout the MDU. Thetransmodulator 20 may instead, or in addition, distribute thetransmodulated signals over wire or via any wireless communicationchannel (including, for example, microwave and optical systems) tohead-ends at any other MDUs or local sites or portions thereof. Ofcourse, the transmodulator 20 may also distribute the transmodulatedsignals directly to IRDs using any desired wireless communicationchannel.

The transmodulator 20 may also receive signals from a cable provider, alocal off-air antenna 44, and/or any other desired signal source such asthose which locally generate A-V channels (e.g., security camerachannels, data networks, or informational channels) using any standardreceiving mechanism such as an antenna, modem or cable connection, andplaces these signals on the cable network 26 for distribution to theIRDs 30-40. These other signals, referred to hereinafter as terrestrialsignals, may comprise any cable, satellite or off-air signal including,for example, standard CATV, UHF, VHF, FM radio signals and/or locallygenerated signals such as security camera or bulletin board channels.The terrestrial signals may be summed or added together in a summingnetwork 46 (which may comprise any standard signal summer) and providedto the transmodulator 20 via a cable line 48, or may be providedseparately to the transmodulator 20. The transmodulator 20 may pass thereceived terrestrial signals to the cable network 26 at the carrierfrequencies at which the terrestrial signals are received, or thetransmodulator 20 may shift some or all of the terrestrial signals infrequency to use the available frequency spectra of the cable network 26more efficiently. Where input terrestrial signals are provided inbase-band, suitable RF modulators may be used.

Preferably, the transmodulator 20 transmodulates the two 500 MHz-wideQPSK-modulated downlink signals into a 128-QAM-modulated signal having32, 6 (or less) MHz-wide channels, wherein each of these channelscorresponds to one of the 32 original transponder signals. It should beunderstood that although 6 MHz channels are convenient and preferred incertain embodiments, other wider or narrower bandwidths may also beemployed. In certain embodiments, for example, bandwidths of less than 6MHz may be employed. The transmodulator 20 may then place each of these32, e.g. 6 MHz-wide, 128-QAM-modulated signals on the cable network 26at any unused or desired carrier frequency bands while, simultaneously,sending the terrestrial signals over the cable network 26 at any otherdesired carrier frequency bands. Alternatively, the transmodulator 20may use any other desired modulation technique to remodulate thereceived satellite signals. As noted above, the transmodulator 20 mayprovide the transmodulated signals and/or the terrestrial signals to theIRDs 30-40 over any wireless network, if so desired.

Each of the IRDs 30-40 receives the 32, QAM-modulated, e.g. 6 MHz-widesignals along with the terrestrial signals from the cable network 26 (orwireless channel) and demodulates at least a user-selected one of thesesignals. Each of the IRDs 30-40 then provides the demodulateduser-selected signal(s) to an output device or processor, such as atelevision set (not shown), for display or processing thereby.

Referring now to FIG. 2, representative methods of combining thetransmodulated transponder signals along with terrestrial signals on thecable network 26 are illustrated. The left-most column of FIG. 2illustrates a previously known method of placing QPSK-modulated signalsalong with terrestrial signals on a cable network. According to thisscheme, all existing terrestrial signals (including cable TV signals)are distributed at, for example, VHF and UHF carrier frequencies below950 MHz while one of the 500 MHz-wide QPSK-modulated signals (associatedwith either the LHCP or the RHCP component of the satellite signal) isplaced directly on the cable network at the unused band between about950 MHz and 1450 MHz. A major problem with this configuration is thatonly the RHCP or the LHCP transponder signals can be placed on astandard cable network at any given time which, in turn, prevents IRDswithin an MDU from decoding or receiving channels associated with theother of the LHCP or the RHCP transponder signals. While this problemcan be overcome by running two cable lines throughout an MDU or byutilizing a high frequency cable plant capable of approximately 2 GHz orgreater bandwidth, these solutions require additional equipment andexpense and are not adaptable to most existing cable plants now in use.Furthermore, the signals provided at the 950 MHz to 1450 MHz band can beseverely degraded by the cable plant due to the poor high frequencypropagation properties of many existing cable plants, especially oldercable plants.

The three right-most columns of FIG. 2 illustrate methods of combiningthe 32, 6 MHz-wide, 128-QAM-modulated signals with existing terrestrialsignals on the cable network 26. The second left-most column of FIG. 2illustrates a configuration in which the transmodulator 20 places the32, 6 MHz-wide, 128-QAM-modulated signals in sequence at a band betweenabout 806 MHz and 998 MHz directly above the common CATV channels. Thisconfiguration can be used with higher grade cable networks thatpropagate signals at up to 1000 MHz without significant degradation.

The third left-most column of FIG. 2 illustrates a configuration inwhich the transmodulator 20 places the 32, 6 MHz-wide, 128-QAM-modulatedsignals at a frequency band between approximately 222 MHz and 414 MHzbetween the CATV or other signals at the VHF and UHF bands. In thiscase, the transmodulator 20 may need to select which terrestrial (e.g.,CATV) signals should be placed in the available portions of the UHF bandabove about 450 MHz and in the available portions of the VHF band belowabout 200 MHz and may need to shift some or all of the chosenterrestrial signals to those bands before placing the transmodulatedsignals on the cable network 26. This frequency distribution techniqueis useful in lower quality cable systems that propagate signals atfrequencies up to about 750 MHz without significant degradation.

The right-most column of FIG. 2 illustrates a configuration in which thetransmodulator 20 places the 32, 6 MHz-wide, 128-QAM-modulated signalsat a number of different spaced-apart frequency bands within theavailable cable network spectra. In particular, the transmodulator 20may break the 32, 6 MHz-wide signals into, for example, eight sets offour, 6 MHz-wide signals and place these eight sets of four signals atthe unused carrier frequency bands between about 375-400 MHz, 475-500MHz and 575-800 MHz, as illustrated in FIG. 2, while sending terrestrialsignals at bands between 50-375 MHz, 400-475 MHz and 500-575 MHz. Thetransmodulator 20 may, however, place these or any other desiredgroupings of the transmodulated signals at any other desired locationswithin the available cable network spectra, including at frequency bandsnormally used by terrestrial signals, based at least in part on how thecable network is being used. In some cases, it may be necessary for thetransmodulator 20 to eliminate or frequency-translate some or all of thereceived terrestrial signals to other frequency bands to avoidinterference with the transmodulated signals.

Referring now to FIG. 3, the transmodulator 20 includes bias tees 50 and52 that receive the RHCP and LHCP QPSK-modulated satellite signals,respectively, at L-band from the LNB 16 (FIG. 1). The bias tee 50provides a 13 volt DC signal to the LNB channel associated with the RHCPsatellite signals, while the bias tee 52 provides a 17 volt DC signal tothe LNB channel associated with the LHCP satellite signal. These DCvoltages provide power to the respective LNB circuitry and select thedesired polarization state in manners well known in the art. In thismanner, standard LNBs configured to select polarization states based onthe applied DC control voltage may be utilized. Other forms of LNBspermanently configured to operate in desired manners may alternativelybe utilized, eliminating the need for the bias tees 50 and 52.

The L-band RHCP and LHCP signals (16 each) are linked to a set of up to32 transmodulator channels, each of which includes a tuner 54, asatellite decoder 56, a packetizer 58, a cable encoder 60, and anupconverter 62. Each transmodulator channel decodes and transmodulatesone of the 32 transponder signals associated with the downlink signal inessentially the same manner and, as a result, the operation of only oneof the 32 transmodulator channels will be described herein. It should beunderstood that a greater or lesser number of transmodulator channelsmay alternatively be provided.

The tuner 54 of a transmodulator channel tunes to one of the transpondersignals associated with either the RHCP or the LHCP signal within theL-band range between 950 and 1450 MHz, while filtering out the other 15transponder signals within that band, to produce a 24 MHz-wide,QPSK-modulated signal corresponding to one of the 32 satellitetransponder signals. If desired, the tuner 54 may shift the tuned 24MHz-wide, QPSK-modulated signal down to base-band.

The satellite decoder 56 decodes the QPSK-modulated transponder signalin known manners to produce a digital signal having a stream of datapackets of programmed-multiplexed data, i.e., a PM signal. In onepresent DTH system, the packets are 130 bytes in length while, inanother common system, the packets are 188 bytes in length. Thesatellite decoder 56 also provides an indication of whether anon-recoverable error has occurred within each of the, for example, 130byte data packets during transmission via the satellite, as will bedescribed in more detail hereinafter. Thereafter, the packetizer 58,which may comprise any specialized or general microprocessing circuitry,repacketizes the data packets into another chosen standard. In aparticular example, 130 byte packets utilized in the DSS® systemstandard, may be repacketized into 188 byte digital video broadcasting(DVB) data packets. These 188 byte DVB data packets are then deliveredto a standard DVB cable encoder 60 such as a Broadcom Corp. BCM3118 I.C.Of course, if the received satellite signals include 188 byte datapackets, the packetizer 58 can be removed. The system can still useerror detecting circuitry that detects if a transmission error hasoccurred during transmission from the satellite and encodes an errorindication into the 188 byte data packets, such as within theReed-Solomon error code associated with those packets. Thus, although arepacketizer is preferred in some systems, it should be understood thatrepacketization is optional, and that other packet sizes and networkstandards could alternatively be utilized.

The DVB cable encoder 60, which may comprise any known DVB encodermodule, modulates the received stream of 188 byte DVB data packetsusing, preferably, a 128-QAM modulation technique, to produce a 6MHz-wide transmodulated signal including all of the audio-visualprograms associated with one of the 32 original transponder signals. The6 MHz-wide transmodulated signal developed by the cable encoder 60 isprovided to an upconverter 62 which shifts the 6-MHz wide transmodulatedsignal to an intermediate frequency (IF), preferably comprising one offour different carrier IFs used by the transmodulator 20. Theupconverter 62 then provides the IF signal to one of eight summers 64associated with the transmodulator 20.

In the configuration of FIG. 3, each of the summers 64 receives an inputfrom four of the upconverters 62, each of which upconverts to adifferent one of the four carrier IFs. Each of the summers 64 combinesthe four received transmodulated signals to produce, for example, one ofthe eight groups of four, 6 MHz-wide transmodulated signals illustratedin the right-most column of FIG. 2. The eight summers 64 of FIG. 3provide eight such groups of four, 6 MHz-wide signals to a variablefrequency upconverter 66 which, in turn, upconverts each of the eightgroups of four, 6 MHz-wide signals to a different carrier frequencyband. As previously noted, bandwidths other than 6 MHz may also beutilized. A summer 68 then combines these upconverted transmodulatedsignals with each other and with any desired frequency-shifted ornon-frequency-shifted terrestrial signals (delivered by a level shifter70) for propagation over the cable network 26 of FIG. 1.

The level shifter 70 may receive signals from an off-air antenna, from acable provider and/or from any other desired signal source (e.g. localsecurity or data services) and pass these signals through to the summer68 at their current carrier frequency, or may shift these signals to oneor more different carrier frequencies for propagation over the cablenetwork 26 using any standard frequency translation or mixer circuitry.The level shifter may contain a power conditioning function to adjustthe level of the received signals to maximize system performance. Ofcourse, if desired, the level shifter 70 may include circuitry similarto the above-described transmodulator channels and transmodulate one ormore of the received terrestrial signals to any desired modulationscheme, such as a 128-QAM scheme, for transmission over the cablenetwork 26. Preferably, such transmodulated terrestrial signals will betransmodulated to the same modulation scheme as the transmodulatedsatellite signals to simplify decoding of the transmodulated terrestrialsignals.

A transmodulator control unit 72, which may be implemented in the formof a microprocessor or any other digital or analog controller,preferably controls the tuners 54, the satellite decoders 56, thepacketizers 58, the cable encoders 60, the upconverters 62, the variablefrequency upconverter 66 and the level shifter 70 in any desired manner.The control unit 72 may control, for example, tuning parameters, such asthe output frequencies of the tuners 54 and may select the frequenciesused by the upconverters 62 and 66 and/or the level shifter 70 tocontrol the carrier frequencies at which the transmodulated signals, aswell as the terrestrial signals, are transmitted over the cable network26.

In a preferred embodiment, the transmodulator control unit 72automatically determines which frequencies to use as carrier frequenciesfor the 32, 6 MHz-wide transmodulated signals (or other transmodulatedsignals) developed by each of the 32 transmodulator channels. In thispreferred configuration, the transmodulator control unit 72 may includea signal detector (not shown) attached to the line 48 upon which theterrestrial signals are received. At start up or at any other desiredtime, the signal detector scrolls through or scans the frequency bandsbetween about 54 MHz and 806 MHz (and higher bands if desired) andchecks the power level and/or tries to tune to standard channellocations to determine which channel locations are being used forterrestrial signals. Typically standard terrestrial channel locationsare spaced 6 MHz apart. If the signal detector detects enough powerand/or is able to tune to a standard channel, e.g., if it tunes to acarrier signal and gets a video sync code, the control unit 72identifies that the band associated with that channel is being used by aterrestrial (e.g., CATV) signal. However, if the signal detector doesnot detect sufficient power and/or is unable to tune to any particularchannel, the band associated with that channel is identified as an emptyband and, therefore, potentially available for use with one or more ofthe transmodulated signals. The control unit 72 may, instead, includeany standard channel or frequency sniffer which locates the frequencybands used by the received terrestrial signals in any other desiredmanner.

After the control unit 72 identifies all of the empty or unusedfrequency bands, this information is preferably stored in non-volatilememory. Operator selection (e.g., by means of a keypad) may also beutilized to select or de-select frequency bands, either alone or inconjunction with an automated system.

The control unit 72 may then, in one embodiment, start at the lowestunoccupied band, determine if this band is wide enough to carry one ormore, i.e., any desired number, of the 32 transmodulated signals and, ifso, identify that band for use by a specific one or more of thetransponder signals by changing the output frequency of, for example,the upconverter 66 associated with those transmodulated signals. Thecontrol unit 72 may go as high as necessary in frequency to assigncarrier frequencies to all 32 of the transmodulated signals.

If the terrestrial signals are spread out throughout the available cablespectra in a manner which makes it impossible or difficult to find emptybands of sufficient predetermined width for all of the desired (e.g.,32) transmodulated signals, the control unit 72 and/or operator inputmay identify one or more of the terrestrial signals and/or the satellitechannels to be eliminated (not provided over the system) or shifted infrequency to thereby produce sufficient regions of continuous spectrumfor use by any desired subsets or groupings of the 32 transmodulatedsignals. In the case in which one or more of the terrestrial signals orthe satellite signals are eliminated, the control unit 72 preferablyselects the one or more signals for elimination based on a predeterminedpriority criterion which may be, for example, input by a user or storedin a memory associated with the control unit 72. The priority criterionmay prioritize the satellite or terrestrial signals for eliminationbased on the channel or frequency at which these signals arrive at thetransmodulator 20 or based on any other desired criteria.

In the embodiment of FIG. 3, the control unit 72 preferably searches forcontinuous 24 MHz-wide unused frequency bands within which to place eachof the eight groups of four, 6 MHz-wide signals developed by the summers64. Alternatively, the control unit 72 could search for any smaller orlarger continuous band of unused frequencies for use in transmitting anyother desired groupings of the 32, 6 MHz-wide transmodulated signals.The control unit 72 may control the level shifter 70 tofrequency-translate the terrestrial signals received at the frequencybands identified for use by the transmodulated signals in anyconventional manner. Also, the control unit 74 may establish acommunication channel with the IRDs 30-40 and signal the location,order, etc. of the transmodulated signals and/or the terrestrial signalsto the IRDs 30-40 over this channel.

A transmodulator control panel 74 is coupled to the control unit 72 and,preferably, includes signal strength measurement devices that indicatethe relative strength of each of the satellite signals and/or each ofthe terrestrial signals input to the transmodulator 20. The controlpanel 74 may also allow an operator to choose default frequencylocations for each of the transmodulated and/or terrestrial signals andmay include controls that permit an installer to select the carrierfrequency bands for any number of the transmodulated and/or terrestrialsignals. Of course, the transmodulator control panel 74 and the controlunit 72 may perform any other desired functions with respect to thetransmodulator 20.

Referring now to FIG. 4, the satellite decoders 56 of FIG. 3 aredescribed in more detail. Each of the satellite decoders 56 may compriseany standard decoder used in decoding the satellite or other signalreceived by the main receiving antenna such as the DSS decodermanufactured by SGS Thomson, commonly referred to as the “Link I.C.,”the Broadcom Corp. BCM4200 decoder chip, or decoder chips manufacturedby LSI Logic and others. Generally, each satellite decoder 56 includes aQPSK demodulator 80 that demodulates the QPSK-modulated signal receivedfrom one of the tuners 54. The QPSK demodulator 80 may use any known ordesired technique to recognize the incoming QPSK symbols and converteach of these symbols into a soft decision presentation of a two bitpattern (e.g., six bits for each three bit soft decision) based on thephase and absolute magnitude of the symbol. The output of the QPSKdemodulator 80 is a digital bit stream comprising a concatenated set oftwo bit patterns (i.e., the six bit soft decision representation ofthese patterns) corresponding to the received QPSK symbols.

Because satellite signals are typically convolutionally encoded beforebeing transmitted via satellite (for error correction purposes), thesatellite decoder 56 includes a convolutional decoder 82 thatconvolutionally decodes, using soft decisions if required, the receivedbit stream in any known manner to produce a stream of 147 byte packetshaving 146 bytes of interleaved data and one sync byte. A sync andde-interleaver 84 detects and strips the sync byte, and thende-interleaves the remaining 146 bytes to produce a stream of 146 bytedata packets, each having 130 bytes of program-multiplexed (PM) data and16 bytes of Reed-Solomon (R-S) error coding (which was added to the datapackets before being transmitted via satellite).

An R-S decoder 88 provides error correction based on the 16 error codedbytes of each of the 146 byte data packets in any known and conventionalmanner to produce a stream of 130 byte error corrected PM data packets.The R-S decoder 88 also determines if a non-correctable error hasoccurred to the data within each of the 130 byte data packets andindicates, via a line 89, whether each 130 byte data packet has correctdata or, alternatively, has data which has been corrupted by anunrecoverable transmission error.

The packetizer 58 (FIG. 3) receives the 130 byte data packets and theassociated error indication and creates therefrom a 132 byte datapacket, having 130 bytes of PM data, one sync byte and one, for example,R-S error code byte indicating whether the 130 bytes of data areerror-free or whether they contain an uncorrected transmission error.The sync and/or error code bytes can also contain other necessarydown-stream information such as command and/or channel configurationinformation.

The packetizer 58 then concatenates the stream of 132 byte data packets,counts off consecutive sets of 187 bytes to form 187 byte data packets,and adds, for example, a byte having an MPEG2 sync code and/or otherdownstream information such as command and channel configurationinformation to the beginning of each of the 187 byte data packets tocreate a stream of 188 byte data packets. An exemplary stream of twelvesuch 188 byte data packets is illustrated in FIG. 5, wherein the MPEG2sync bytes are illustrated as “47”, hexadecimal, the sync bytesassociated with each of the 130 bytes of data are illustrated as “1D”hexadecimal and the R-S error code or error flag byte associated witheach of the 130 bytes of data are illustrated as “94” hexadecimal forthe “no error” condition and may be, for example, “95” hexadecimal (notshown) for the error condition. As will be evident from FIG. 5, each ofthe 132 byte packets having 1 sync byte, 1 error flag byte and 130 bytesof program-multiplexed data can be fully contained within one 188 bytepacket or can be split between two 188 byte packets for transmissionover the cable network 26. As will also be evident, the pattern of thetwelve 188 byte packets of FIG. 5 repeats for every seventeen 130 bytepackets.

The packetizer 58 delivers the stream of 188 byte data packets to anassociated one of the cable encoders 60. Although the packetizer 58 isdescribed herein as converting from 130 to 188 byte data packets, thepacketizer 58 could convert between data packets of any other number ofbytes to accommodate other signal decoders, cable encoders, or dataorganization schemes as desired.

Referring now to FIG. 6, the cable encoders 60 of FIG. 3 are describedin more detail. Each cable encoder 60 may comprise any standard DVBcable encoder, such as a DVB encoder of the type manufactured byBroadcom Corp. (the BCM3033 I.C.) which, as is known in the art,operates on 188 byte data packets having 187 bytes of data and one syncbyte. Each cable encoder 60 includes a scrambler 90, which randomizesthe bits/bytes within each of the 188 byte data packets, and an R-Sencoder 92 which adds an R-S error code of, for example, 16 R-S paritybytes, to each of the scrambled 188 byte data packets. Thereafter, astandard interleaver 94 interleaves groups of the R-S encoded datapackets for transmission error resistance purposes, as is generallyknown in the art. A byte to m-tuple encoder 96 splits up the interleaveddata packets into consecutive sets of m bits for encoding using a QAMmodulation technique. The value of m is a function of the level of QAMmodulation being used and, specifically, the QAM modulation techniquecan be expressed as 2^(m)-QAM. Thus, for example, m equals seven in128-QAM while m equals 4 in 16-QAM.

A differential encoder 98 differentially encodes the two mostsignificant bits of each of the m-tuple bit packets using any commonlyknown differential encoding technique, as is commonly performed in QAMmodulation. Next, a square-root raised cosine filter 100 provides apulse shaping feature to the differentially encoded bit packets anddelivers the shaped pulses to, for example, a 128-QAM modulator 102which may comprise any standard QAM modulator that produces a 128-QAMmodulated signal at the output thereof.

While the transmodulator 20 is described herein as including apacketizer 58 which repacketizes 130 byte data packets produced by astandard DSS satellite decoder 56 into standard 188 byte data packetsused by systems following the DVB transmission standard to enable theuse of known DSS satellite decoders and known DVB cable encoders, thetransmodulator 20 could, instead, include circuitry specificallydesigned to encode the 130 byte data packets produced by the satellitedecoder 56 in a manner similar to the DVB cable encoder, i.e., byscrambling, R-S encoding, interleaving, etc. the 130 byte data packetsto produce the 128-QAM modulated signals.

Furthermore, while the signal distribution system 10 is described hereinas using a 128-QAM modulator 102, any other type of QAM modulator, suchas an 8-QAM, 32-QAM, or higher order QAM modulator can be used to encodethe decoded satellite signal, with the choice being dependent on howmuch frequency spectrum is available on a particular cable system and onhow noisy the cable network tends to be which, in turn, drives the levelof error protection required. In general, the higher the order of QAMencoding, the less frequency spectrum will be necessary to transmit thedesired number (e.g., 32) satellite transponder signals (or othersignals) over a cable network. However, the higher the order of QAMmodulation, the more the transmodulated signals will be susceptible tonoise while being transmitted over a cable network. Likewise, differentones of the transmodulator channels of FIG. 3 may transmodulate thereceived PM signal, i.e., the tuned transponder signal, using differentmodulation schemes. For example, a first set of the transmodulatorchannels may remodulate PM signals using a 128-QAM modulation technique,while a second set of transmodulator channels may use a 32-QAMmodulation technique, a 64-QAM modulation technique, and so on. Thechoice of the modulation technique for any particular transmodulatorchannel may depend on, for example, the data rate of the PM signal beingreceived, as well as other factors.

Furthermore, as noted above, modulation techniques besides QAM can beused when transmodulating the decoded satellite signal. Other suchmodulation techniques may include, for example, any high rate digitalmodulation techniques such as VSB (vestigial side band), including8-VSB, 16-VSB etc., or QAM with trellis-coded modulation. Othermodulation techniques which may be developed in the future couldsimilarly be used without departing from the spirit and scope of thepresent invention. In general, the choice of a modulation technique willbe driven by the reduction in bandwidth which must be accomplished bythe modulation technique and by the noise susceptibility of themodulation technique. If a different modulation technique is used,however, it is understood that a different type of cable encoder will benecessary to properly transmodulate the desired transponder signals (orother received signals) for propagation over the cable network 26.

Likewise, it is understood that signals other than QPSK modulatedsignals can be received at the main signal receiver 14 (or otherreceiver) and transmodulated for delivery over the cable network 26using the concepts described herein. In this situation, the particularsof the transmodulator 20 will change based on the type of modulation,carrier frequencies and transmission formats associated with thesedifferent received signals. It is considered that the use of an 8-PSK(phase shift keying) modulation scheme for encoding the satellite signaland a 16-QAM or higher order QAM (32-QAM, 64-QAM etc.) scheme forencoding the cable signal may be one useful combination. It is alsoconsidered that the use of a 16-QAM scheme for encoding the satellitesignal and a 32-QAM or higher order QAM scheme for encoding the cablesignal may be another useful combination.

Referring now to FIG. 7, the circuitry associated with each of the IRDs30-40, identified hereinafter as IRD 30, is illustrated in block format.While the IRD 30 will be described herein as an IRD which decodes DSSsignals, it will be understood by those skilled in the art that the IRD30 may comprise any other standard circuitry that decodes any other typeof modulated or encoded signals.

The IRD 30 may initially scan all the channels from, for example, lowcarrier frequencies to high carrier frequencies, to locate the frequencybands or channels used by the 32 transmodulated signals and then assignchannel numbers to these located signals based on a predeterminedordering scheme used by the transmodulator 20. However, thetransmodulator 20 may actively signal the channel locations, ordering,frequency assignments, etc. of the transmodulated satellite signalsand/or terrestrial signals via a communication channel established over,for example, the cable network 26. Such a communication channel maycomprise a low-speed channel that uses uncoded bits of the sync anderror code bytes within the, for example, 188 byte data packets, and maybe used to deliver any desired information to the IRD 30 over time,i.e., using a large number of the 188 byte data packets. For example, aspreviously discussed, side data may be transmitted via the cable network26 including a frequency map for the transmodulated signals. In thisinstance, once an IRD has located (e.g. by scanning) a first of thetransmodulated signals, it may then access the frequency map to identifythe frequencies utilized by the transmodulator 20 for all of theremaining channels. This operation will substantially increase the speedof the initialization process of an IRD at power-up. Periodic updates ofthe frequency map may also be included in the side data.

The IRD 30 includes a down-converter and tuner 110 connected to thecable network 26. The down-converter is used, if necessary, to shifthigher frequency 6 MHz channels to lower frequencies commonly supportedby standard tuners. The tuner 110 is responsive to a controller (notshown) and tunes to the frequency band associated with a selected one ofthe 6 MHz-wide transmodulated signals. The tuned signal is provided to adecoder 112, which may comprise a standard DVB cable decoder such as theBCM3118 decoder chip manufactured by Broadcom Corp. Generally, thedecoder 112 includes a 128-QAM demodulator that demodulates the QAMtransmodulated signal to produce a set of interleaved, R-S encoded datapackets. A de-interleaver de-interleaves the data packets and,thereafter, an R-S decoder strips off the error coding and, to theextent possible, corrects errors resulting from transmission over thecable, to produce a stream of 188 byte data packets. Thereafter adescrambler descrambles each of the 188-byte data packets to remove theeffects of the scrambler 90 of FIG. 6. The DVB cable decoder 112delivers the stream of 188 byte data packets, each having 187 bytes ofdata and one sync byte, to a packetizer 114 while, simultaneously,providing an indication of whether the data associated with each of the188 byte data packets has experienced a non-recoverable error duringtransmission over the cable network 26. This indication may be developedby the R-S decoder of the DVB decoder 112 and provided to the packetizer114 via, for example, a line 115.

The packetizer 114 strips off the sync byte of each of the 188 byte datapackets to produce a stream of 187 byte data packets, concatenates thestream of 187 byte data packets and repacketizes the data stream into astream of 132 byte data packets, each having 130 bytes ofprogram-multiplexed data, one sync byte and one error code byte. Usingthe error indication produced by the DVB cable decoder 112 (on line115), the packetizer 114 determines if a non-recoverable error hasoccurred with respect to any of the 188 byte packets within which anyportion of each 132 byte data packet was included. If so, the error codeof the 132 byte data packet is changed to reflect that the 132 byte datapacket contains corrupted data.

As a result of this operation, the signal distribution system 10includes two layers of error coding and is capable of detectingunrecoverable transmission errors which occur during transmission fromthe satellite base station to the transmodulator 20, and/or from thetransmodulator 20 to the IRD 30. In particular, the packetizer 58 (ofthe transmodulator 20) codes the 132 byte data packets with errorinformation indicating if a transmission error has occurred during thesatellite transmission stage of broadcast and packetizes this error codeas data within the 188 byte data packets transmitted over the cablenetwork 26. The R-S decoder in the IRD detects if a non-recoverableerror has occurred to each of the 188 byte data packets duringtransmission over the cable network 26 and combines this informationwith the error code indicated in the error code byte of each 132 bytepackage to indicate to the later stages of the decoder whether or noteach 132 byte packet is correct or contains an error. It should beunderstood that other packet schemes may similarly be used. For example,if the IRD transport decoder (discussed below) is configured to process,e.g., 188 byte data packets, both the packetizer 114 and the errorcoding function of the packetizer 114 may not be required.

It should be noted that, using the transmodulation and decoding schemedescribed above, the integrity and security of each PM signal isreserved. That is, the data packets associated with each received PMsignal are preserved during the transmodulation and decoding procedures.

The output of the packetizer 114 is provided to a splitter 116 whichstrips the 130 bytes of program-multiplexed data from the 132 byte datapackets using a smoothing buffer to minimize packet-to-packet delayvariation or jitter and provides this data to a transport decoder 118.The splitter 116 also decodes the error code associated with each of the132 byte data packets and indicates to the transport decoder 118 if the130 bytes of program-multiplexed data at the input thereof have beencorrupted during transmission via either the satellite or the cable.

The transport decoder 118, which may comprise any standard transportdecoder such as those associated with the DSS system, decodes theprogram-multiplexed data to produce a stream of digital data. If thepresence of an uncorrected error is indicated for any data packet, thetransport decoder 118 may use that information to begin known errorconcealment techniques to reduce the effects of the error when the finalsignal is, for example, displayed on a television screen. If, however,the error code associated with any particular 130 byte data packetindicates that no transmission error has occurred therein, the transportdecoder 118 strips off all data which is not an actual part of thesignal to produce a program-multiplexed signal having data associatedwith from approximately five to eight individual A-V programs, all inknown manners.

The program multiplexed data is provided to a demultiplexer 120 which isalso responsive to the controller (not shown). The demultiplexer 120,which may be any standard demultiplexer, extracts one of the five toeight A-V programs from the program multiplexed data signal and providesa data stream having data pertaining to the extracted program (asidentified by the controller) to a decoder having an MPEG video decoder122, an MPEG audio decoder 123 and a data processor 124.

The MPEG video decoder 122, which may be any standard MPEG2 videodecoder commonly known in the art, operates to produce a digital videosignal from the received bit stream and provides this digital signal toan NTSC encoder 125. The NTSC encoder 125, which may be any standardencoder, converts the received digital signal into an analog NTSC videosignal and provides this signal to a television set 126 for display onthe television screen, as is commonly known in the art. The MPEG audiodecoder 123, which may be any standard audio decoder commonly known inthe art, produces a digital audio signal from the received bit stream,and provides this audio bit stream to a D/A converter 127 which, inturn, provides an audio signal to the television set 126 for use inconjunction with the video signal developed by the NTSC encoder 125. Thedata processor 124 performs independent data processing or datafunctions on data within the decoded signal. The data processor 124 may,for example, decode, display and/or run web pages, software programs,etc. delivered via the satellite communication channel. In addition orin the alternative, other video, audio and/or data signals may beprocessed or output in known manners. Likewise, terrestrial signals maybe diplexed off of the cable network 26 and provided to a tunerassociated with a user television, VCR, etc. for demodulation in mannersknown in the art.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only, and notto be limiting of the invention, it will be apparent to those ofordinary skill in the art that changes, additions and/or deletions maybe made to the disclosed embodiments without departing from the spiritand scope of the invention.

What is claimed is:
 1. A signal distribution system for distributing anerror-encoded communication signal over a communication channel, thesignal distribution system comprising: a receiver that receives a firsterror-encoded communication signal; a decoder that decodes the receivedfirst error-encoded communication signal to produce a data signal and anerror indication that indicates whether an uncorrected transmissionerror is present in the data signal; a signal encoder that produces asecond error-encoded communication signal including information relatedto both the data signal and the error indication; and a transmitter thattransmits the second error-encoded communication signal over thecommunication channel.
 2. The signal distribution system of claim 1,further including a combiner that combines the error indication with thedata signal to produce a combined signal.
 3. The signal distributionsystem of claim 2, further comprising a receiver unit coupled to thecommunication channel, wherein the receiver unit includes a furtherdecoder that decodes the second error-encoded communication signal toproduce the error indication, the data signal, and a further errorindication that indicates whether an uncorrected error is present in thedata signal as a result of transmission over the communication channel,and an error detector that detects the presence of an error within thedata signal based on the error indication or the further errorindication.
 4. The signal distribution system of claim 1, wherein thefirst error-encoded communication signal is modulated according to afirst modulation scheme, and wherein the transmitter includes amodulator that modulates the second error-encoded communication signalaccording to a second modulation scheme.
 5. A method of distributing anerror-encoded communication signal over a communication channel,comprising the steps of: receiving a first error-encoded communicationsignal; decoding the first error-encoded communication signal to producea data signal and an error indication that indicates whether anuncorrected transmission error is present in the data signal; producinga second error-encoded communication signal including informationrelated to both the data signal and the error indication; andtransmitting the second error-encoded communication signal over thecommunication channel.
 6. The method of distributing an error-encodedcommunication signal over a communication channel according to claim 5,further including the step of combining the error indication with thedata signal.
 7. The method of distributing an error-encodedcommunication signal over a communication channel according to claim 5,further including the steps of receiving the second error-encodedcommunication signal from the communication channel, decoding thereceived second error-encoded communication signal to derive the errorindication, the data signal, and a further error indication thatindicates whether an uncorrected error is present in the data signal asa result of transmission over the communication channel, and detectingthe presence of an error within the data signal based on the errorindication or the further error indication.
 8. The method ofdistributing an error-encoded communication signal over a communicationchannel according to claim 5, wherein the first error-encodedcommunication signal is modulated according to a first modulationscheme, and further including the step of modulating the seconderror-encoded communication signal according to a second modulationscheme prior to the step of transmitting.